The moon was once home to spectacular 'fire fountains', similar to those seen in Hawaii today.

The Apollo missions found remnants of these lava fountains in tiny beads of volcanic glass on the moon.

Now, US scientists believe they have identified the volatile gas that drove those eruptions, finally solving the mystery to how they formed.

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Scientists have found traces of carbon in volcanic glass collected from the Apollo missions to the moon. The finding may explain the driving force behind ancient 'fire fountain' eruptions. Pictured are tiny pieces of molten magma that became trapped in tiny crystals of olivine, preserving evidence of volatile gasses

HOW DID FIRE FOUNTAINS FORM?

The moon's surface was hot and magma often bubbled up from below and broke the surface.

Lava associated with lunar fire fountains contained significant amounts of carbon, according to new research.

As it rose from the lunar depths, that carbon combined with oxygen to make substantial amounts of carbon monoxide (CO) gas.

Carbon, as it combines with oxygen to form CO gas, would have degassed before other volatiles.

The CO gas was responsible for the fire fountains that sprayed volcanic glass over parts of the lunar surface.

Fire fountains, a type of eruption that occurs frequently in Hawaii, require the presence of volatiles mixed in with the erupting lava.

Volatile compounds turn into gas as the lavas rise from the depths.

That expansion of that gas causes lava to blast into the air once it reaches the surface, a bit like taking the lid off a shaken bottle of Pepsi.

'The question for many years was what gas produced these sorts of eruptions on the moon,' said Alberto Saal, associate professor of Earth, environmental, and planetary sciences.

'The gas is gone, so it hasn't been easy to figure out.'

The research, published in Nature Geoscience, suggests that lava associated with lunar fire fountains contained significant amounts of carbon.

As it rose from the lunar depths, that carbon combined with oxygen to make substantial amounts of carbon monoxide (CO) gas.

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That CO gas was responsible for the fire fountains that sprayed volcanic glass over parts of the lunar surface.

For many years, the moon was thought to be devoid of volatiles like hydrogen and carbon.

It wasn't until the last decade or so that volatiles were definitively detected in lunar samples.

In 2008, Saal and colleagues detected water in lunar volcanic beads. They followed that discovery with detections of sulphur, chlorine and fluorine.

The discovery also suggests that some volatile elements on the moon and Earth have a common origin. Pictured is

While it became apparent that the moon was not completely depleted of volatiles as was once thought, none of the volatiles that had been detected were consistent with fire fountain eruptions.

For example, if water had been the driving force, there should be mineralogical signatures in recovered samples. There are none.

For this research, Saal and his colleagues carefully studied glass beads brought back to Earth from the Apollo 15 and 17 missions.

In particular, they looked at samples that contained melt inclusions, tiny dots of molten magma that became trapped within crystals of olivine. The crystals trap gases present in the magma before they can escape.

Erik Hauri from Carnegie Institution for Science developed a state-of-the-art ion probe technique reducing the detection limits of carbon by two orders of magnitude.

That allows a measurement of as low as 0.1 part per million.

Fire fountains, a type of eruption that occurs frequently in Hawaii (pictured), require the presence of volatiles mixed in with the erupting lava

'This breakthrough depended on the ability of Carnegie's NanoSIMS ion probe to measure incredibly low levels of carbon, on objects that are the diameter of a human hair,' said Hauri.

'It is really a remarkable achievement both scientifically and technically.'

Researchers believe carbon, as it combines with oxygen to form CO gas, would have degassed before other volatiles.

'Most of the carbon would have degassed deep under the surface,' Saal said.

'Other volatiles like hydrogen degassed later, when the magma was much closer to the surface and after the lava began breaking up into small globules.

'That suggests carbon was driving the process in its early stages.'

This Nasa image shows the moon coalescing from debris created when a Mars-size object hit into the early Earth. Carbon found in lunar samples suggests the moon's surface was very similar to our own planet's

The findings also serve as more evidence that some volatile reservoirs in the moon's interior share a common origin with reservoirs in the Earth, the researchers say.

The amount of carbon detected in the melt inclusions was found to be very similar to the amount of carbon found in basalts erupted at Earth's mid-ocean ridges.

This implications for understanding the moon's origin.

Scientists believe the Moon formed when Earth was hit by a Mars-size object very early in its history. Debris from that impact accreted to form the moon.

'The volatile evidence suggests that either some of Earth's volatiles survived that impact and were included in the accretion of the moon or that volatiles were delivered to both the Earth and moon at the same time from a common source - perhaps a bombardment of primitive meteorites,' Saal said.